1. Field of the Invention
The present invention relates to a paste for a dye-sensitized solar cell, a transparent insulation film for a dye-sensitized solar cell, a dye-sensitized solar cell, and a method of fabricating a dye-sensitized solar cell.
2. Description of Related Art
Conventionally, there is known a dye-sensitized solar cell having such a configuration that a dye-supported semiconductor layer (photoelectric conversion layer) formed of titanium oxide or the like and an electrolyte layer are provided between a transparent electrode and a counter electrode having a catalyst-supported conductive layer, and the peripheries thereof are sealed with a sealant such as a resin (for example, JP-A-2005-228594 (KOKAI)). Furthermore, there is known a dye-sensitized solar cell having a sequential stack configuration of a dye-supported semiconductor layer (photoelectric conversion layer) formed of titanium oxide or the like similarly as above, an insulating reflection layer, a catalyst layer and a conductive layer in this order on a transparent electrode (for example, JP-A-2003-142171 (KOKAI)).
Furthermore, for the purpose of realizing the enlargement of the area of a dye-sensitized solar cell, serial connection has recently been attempted between a solar battery cell (F cell) having a sequential stack of a dye-supported semiconductor layer (photoelectric conversion layer) formed of titanium oxide or the like, an insulating reflection layer, a catalyst layer and a conductive layer in this order on a transparent electrode, and a solar battery cell (R cell) having a sequential stack of a catalyst layer, a transparent insulation film, a dye-supported semiconductor layer (photoelectric conversion layer) formed of titanium oxide or the like, and a conductive layer in this order on the transparent electrode (for example, JP-A-2007-18809 (KOKAI)). In addition, the above-stated stack structure constituting an F cell and the above-stated stack structure constituting an R cell are isolated from each other by a partition wall.
In the case of a dye-sensitized solar cell constituted from an F cell and an R cell which are connected in series with one another, the light-receiving surface is set on the transparent electrode side, and a light is incident into the corresponding cells from the transparent electrode side. In order to ensure that electric power is generated by photoelectric conversion in the F cell and R cell, the above-stated incident light must reach the corresponding semiconductor layers (photoelectric conversion layers) in the corresponding cells so as to realize light absorption in the cells by means of dyes supported on the respective semiconductor layers.
In the case of the F cell, since the semiconductor layer is directly formed on the transparent electrode, alight incident from the transparent electrode side reaches the semiconductor layer relatively easily so that an intended light absorption is relatively easily carried out by the supported dye. On the other hand, in the case of the R cell, since the catalyst layer and the transparent insulation film are interposed between the transparent electrode and the semiconductor layer, a light incident from the transparent electrode side reaches the semiconductor layer through the catalyst layer and the transparent insulation film. In such an R cell, therefore, in order to enhance the light amount of the incident light reaching the semiconductor layer, it is particularly important to improve the transparency of the transparent insulation film.
In order to meet such requirement, JP-A-2007-18809 (KOKAI) secures the transparency of the transparent insulation film by rendering the transparent insulation film porous.
In the case of the above-stated R cell, the dye-supported semiconductor layer is formed after the formation of the transparent insulation film. However, the support of the dye on the semiconductor layer is carried out by dipping the semiconductor layer in a dye solution. As a result, the transparent insulation film in addition to the semiconductor layer is also dipped in the dye solution, so that the dye is also adsorbed at a certain degree into the transparent insulation film. Therefore, since the above-stated incident light is absorbed at a certain degree by the transparent insulation film, the ratio of the incident light reaching the semiconductor layer is decreased, so that the photoelectric conversion efficiency in the semiconductor layer, that is, the electric power generation efficiency of a dye-sensitized solar cell is deteriorated.
From the viewpoint of these problems, JP-A-2007-18809 (KOKAI) discloses the formation of the transparent insulation film by using fine particles, such as silicon oxide, onto which a dye is not readily adsorbed. Furthermore, the same publication discloses an attempt to form, on the surface of fine particles as a base material, a coated film made of magnesium oxide or the like soluble in an acidic solution, thereby forming the transparent insulation film using fine particles such as titanium oxide. In this case, when the transparent insulation film is dipped in the above-stated dye solution, the dye is adsorbed into the coated film, so the coated film is then dipped in the acidic solution to remove the coated film so as to eliminate the dye, thereby obtaining a transparent film.
In the transparent insulation film obtained through the dye removing process, however, the dyes adsorbed onto the soluble fine particles become useless in terms of resources. Furthermore, there has been a need for further improving the transparency by decreasing the dye adsorption amount.
Patent Reference 1: JP-A-2005-228594 (KOKAI)
Patent Reference 2: JP-A-2003-142171 (KOKAI)
Patent Reference 3: JP-A-2007-18809 (KOKAI)